Principles of Genetics and Breeding

13.1.7.2. Heterosis

The word heterosis was coined by Shull (1914) to describe the increased vigour of crossbreds relative to their parents.

The heterosis is observed when the animals of different genetic backgrounds (lines, strains, breeds, etc.) are mated and this mating system is called the line crossing or cross breeding. The commercial purposes of crossbreeding are mainly two fold.

- to take the advantage of heterosis (hybrid vigour) which requires heterozygosity. The heterotic effect is non-additive genetically.

- To combine good qualities of two or more breeds. viz., combination of better quality of disease resistance as well as the adaptation of zebu breeds of cattle and the high milk producing capacity of exotic breeds.

- The heterosis is defined as the amount by which the mean of F₁ generation exceeds to its better parent.